1. Field of the Invention
The present invention relates in general terms to rotary electrical machines, and in particular to a synchronous rotary machine having a permanent magnet rotor, such as an alternator or alternator-starter for a motor vehicle.
2. Description of Related Art
It is already known in the state of the art to provide rotary machines in which the rotor has a set of permanent magnets, which are for example arranged on the surface or inset a certain distance below the surface of the rotor, so as to define an appropriate pattern of South and North poles.
Because the excitation of such a machine is imposed permanently by the rotor magnets, it is necessary to provide, in the case of an alternator, arrangements for adjusting the electrical power delivered by the machine to output load: in this connection, power output is currently linked to loads in which consumption varies over time.
In the case of motor vehicle alternators, the load connected to the armature of the alternator can, in this context, vary greatly, and may even be zero or substantially zero while the inductive rotor of the alternator is in motion.
In order to adjust the electrical power delivered by the rotary machine, one known solution consists in interposing magnetic defluxing parts between the magnets of the rotor in order to channel part of the magnetic flux flowing between the rotor and the stator. This defluxing flux does not contribute to the generation of current by the windings of the stator armature. The intensity of this flux adjusts itself as a function of the load imposed on the armature output.
One known defluxing solution is accordingly illustrated in FIG. 1, in which a rotor 20 comprises magnets 22S which define South poles, and magnets 22N defining North poles, arranged alternately. This known solution consists in interposing between each pair of adjacent magnets a magnetic defluxing piece 25, these pieces being adapted to cooperate with the poles of the stator in order to produce defluxing.
Also illustrated, in FIG. 2 in a developed form, is the diagrammatic behaviour of this rotor in cooperation with a stator 10 having teeth 16 delimited by slots 14 which contain armature windings 18, with an induced flux F1 created by the magnets and an inverse defluxing flux FD. It will be noted in this Figure that the induced flux and the defluxing flux are poorly individualised. It has been found that this partial superimposition on each others induced fluxes and the defluxing fluxes flowing in opposite directions, limits the defluxing capacity of the machine, and therefore the range of possible excitations of the machine.
The object of the invention is to enable rotary machines to be made which deliver electrical energy that is optimised as a function of the load connected to the armature of the machine.
In order to achieve this object, the invention proposes a rotary electrical machine, comprising a stator having at least one armature winding located in slots defining stator poles, and a rotor mounted for rotation inside the stator, the rotor having at its outer periphery magnetic poles comprising, firstly, North-South magnets, and secondly, magnetic reluctance pieces, wherein the North-South magnets of two consecutive poles n, n+1 are grouped side by side, and in that the magnetic reluctance pieces of two consecutive poles n+1, n+2 are also side by side.
In order to achieve the said object, the invention also proposes a rotary electrical machine, comprising a stator having a single armature winding located in slots defining stator poles, and a rotor mounted for rotation inside the stator, the rotor having at its outer periphery magnetic poles comprising, firstly, North-South magnets, and secondly, magnetic reluctance pieces, wherein the North-South magnets of two consecutive poles n, n+1 are grouped side by side, and in that the magnetic reluctance pieces of two consecutive poles n+1, n+2 are also side by side.
Thanks to the invention, high quality defluxing is obtained in the machine, because the flux induced by the magnets on the one hand, and the defluxing flux on the other hand, are individualised better than in the known versions. It has also been found that this arrangement has the advantage that it leads to a reduction in variations of torque during operation of the machine.
Preferred but not limiting aspects of the rotary machine according to the invention are as follows:
the stator includes an excitation winding which is fixed around the stator, the stator having two magnetic parts separated by a non-magnetic region in line with the excitation winding on the inner side of the latter,
a magnetic member is arranged, surrounding the said magnetic parts of the stator and in contact with them, in such a way as to enable the said magnetic path to be closed in the stator, the said magnetic member having a slot for receiving the excitation winding,
the axial width of the non-magnetic region is substantially greater than the width of the airgap separating the rotor from the stator,
the magnets of the rotor are disposed asymmetrically with respect to the centre plane transverse to the axis (X) of rotation of the rotor which is situated in line with the excitation winding,
the magnets of the rotor occupy a space the width of which, in a direction tangential to the rotor, varies with displacement in a direction parallel to the axis (X) of rotation of the rotor,
the said at least one global excitation winding is connected to a variable electrical power supply such that the magnetic flux generated by the said global excitation winding is able to reinforce the fluxes induced between the rotor and the stator,
means are provided for reversing the sign of the power supply of the global excitation winding, in such a way that the magnetic flux generated by the global excitation winding reduces the fluxes induced in the stator,
the rotor has, in its tangential direction, a distribution of polar parts with a permanent magnet or magnets, the or each magnet defining two poles the polarity of which is imposed by a magnet or magnets, and polar reluctance parts each defining two poles having free polarities,
the magnets are magnets with essentially radial flux,
the magnets are ferrite magnets,
the magnets are rare earth magnets,
the magnets are ferrite and rare earth magnets,
the rotary electrical machine consists of a motor vehicle alternator-starter.